Looping over an array of objects and creating an array for each item with the same value at a certain index

Question

I need to create an array that contains all the visits values if the date is the same without creating duplicate date arrays

const MOCK = {
        data: [
          {date: "Aug.03", name: "Nihal Pandit", visits: 3 },
          {date: "Aug.03", name: "Anthony Elias", visits: 3 },
          {date: "Aug.04", name: "Alex P.", visits: 2 },
          {date: "Aug.05", name: "Alex P.", visits: 3 },
          {date: "Aug.05", name: "Anthony Elias", visits: 3 },
        ]
     }

But im not sure of a method that lets you compare the values from one iteration to another when looping over an array. I think Array.reduce() might work, but I dont understand how to properly use reduce at this point.

I am looking for a result that looks like:

[["Aug.03", 3, 3], ["Aug.04",2],["Aug.05", 2, 3]

So I need an array for each date (the array should contain that date) and all the visit values from every object that contains that date.

let newArray = []
let visitCountValues = MOCK?.data?.map((item, idx)=> {
        let value = Object.values(item);
      if(value[0] === value[0]){
        newArray.push([value[0], value[1])
      }
        
      })

Could you share the expected result and your try on the solution as well? — Maniraj Murugan
– Maniraj Murugan, Commented Aug 18, 2022 at 14:35

Mina · Accepted Answer · 2022-08-18 14:59:29Z

2

You can use reduce to group the array on one objectwithdateas property, andObject.valuesto get themapped` arrays.

const MOCK = {
        data: [
          {date: "Aug.03", name: "Nihal Pandit", visits: 3 },
          {date: "Aug.03", name: "Anthony Elias", visits: 3 },
          {date: "Aug.04", name: "Alex P.", visits: 2 },
          {date: "Aug.05", name: "Alex P.", visits: 3 },
          {date: "Aug.05", name: "Anthony Elias", visits: 3 },
        ]
     }
     
const dateGroups = Object.values(MOCK.data.reduce((acc, { date, visits }) => ({
  ...acc,
  [date]: [...(acc[date] || [date]), visits]
}), {}))

console.log(dateGroups)

edited Aug 18, 2022 at 14:59

answered Aug 18, 2022 at 14:43

Mina

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R4ncid · Accepted Answer · 2022-08-18 14:49:23Z

2

after you update you question I understood better you can do something like this

const visits = [
      {date: "Aug.03", name: "Nihal Pandit", visits: 3 },
      {date: "Aug.03", name: "Anthony Elias", visits: 3 },
      {date: "Aug.04", name: "Alex P.", visits: 2 },
      {date: "Aug.05", name: "Alex P.", visits: 3 },
      {date: "Aug.05", name: "Anthony Elias", visits: 3 },
    ]
    
const result = Object.values(visits.reduce((res, {date, visits}) =>{
   const existing = res[date] || [date]
   res[date] = [...existing, visits]
   return res
}, {}))

console.log(result)

edited Aug 18, 2022 at 14:49

answered Aug 18, 2022 at 14:43

R4ncid

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